The invention relates to a novel process of making liquid antacid calcium carbonate containing compositions for neutralizing stomach acid (and calcium source or calcium nutritional supplement) in humans and other animals.
Liquid pharmaceutical compositions for delivery of an antacid are generally of the suspension form. They constitute a finely divided antacid active, in solid form which is suspended in a liquid medium. These compositions generally are alkaline, with typical pH values in the range of 7.5 to 8.7.
One problem faced by such liquid compositions is that the pH may drift either below or over the 7.5 to 8.7 pH limits due to equilibrium not being established within 24 hours between the carbonate salt and its environment. This results in such things as color changes if a pH sensitive dye is used, possible microbial growth, and acceleration of base catalyzed degradations.
One method which has been used to stabilize such a suspension is described in U.S. Pat. No 5,498,426, Wilson et al., which includes an alkali metal phosphate salt, and alkali metal bicarbonate salt in addition to the alkaline earth carbonate salt.
Another group of patents to Beyerle et al., U.S. Pat. No. 5,631,026 and U.S. Pat. No. 5,455,050 include with the calcium carbonate a magnesium carbonate and/or magnesium trisilcate as well as a carboxylic acid pH adjusting agent.
U.S. Pat. No. 5,002,777 discloses a concentrated suspension of calcium carbonate in a liquid carrier contained in a capsule, in which the liquid carrier is PEG 400.
The problem faced by the pH drift has not been successfully solved for liquid antacid compositions which are magnesium or aluminum free. The present invention is the recognition of this problem and a solution to such whereby a pleasant liquid antacid formulation is achieved which is pH stable.
The present invention is to a process of making an aluminum and magnesium free liquid antacid formulation which is stable at a pH from about 7.5 to about 8.7. The liquid antacid formulation is also free from antimicrobial contamination during the stable shelf life of the product.
The aluminum and magnesium free antacid formulation is a calcium carbonate aqueous antacid suspension having a pH of about 7.5 to about 8.7, which suspension is prepared by a process which comprises the steps of:
a) adding to water an effective amount of particulate calcium carbonate with mixing until the particulate is completely wetted and dispersed; and
b) adding to said mixture of part a) with stirring an amount of a suspending agent for a time sufficient to substantially coat said particulate material, and to produce a suspension; or alternately adding b) to a) and;
c) while stirring, titrating the suspension of part b) with a pH adjusting agent to provide a pH of about 6.4 to 7.0 to the aqueous antacid suspension.
The present invention is also directed to a liquid antacid pharmaceutical formulation for neutralizing excess stomach acid. The present invention is also a method of orally administering to a mammal in need of such treatment an effective amount of said liquid antacid composition.
The aqueous suspensions of the present invention have been found to be a stabilized liquid calcium carbonate containing antacid having a pH range of about 7.5 to about 8.7, meeting USP standards. The suspensions of this invention have been found to be stable with regard to antimicrobial, viscosity, defoaming, and acid neutralizing capacity (ANC) parameters, as well as to pH. The present invention has found that the selective order of addition and mixing of the essential components herein provides the stable pH of this suspension and further provides for the formation of a higher concentrated suspension of calcium carbonate than previously available to the marketplace. The higher dose formulation of liquid calcium carbonate, in addition to providing maximum acid neutralizing capacity, may also provide a 1000 mg of calcium per dosage to a mammal in need of such calcium for building bone, for treatment of osteoporosis, for pre-menstrual syndrome, etc.
The present invention is to an aqueous antacid suspension for oral use having a pH of about 7.5 to about 8.7 of calcium carbonate, prepared by a process which comprises:
a) adding to water an effective amount of calcium carbonate with mixing until the calcium carbonate is completely wetted and dispersed; and
b) adding to said mixture of part a) with stirring a suspending agent for a time sufficient to substantially coat said carbonate, and to produce a suspension; alternatively, the suspending agent may be added to water first, and calcium carbonate adding second; and
c) while stirring, titrating the suspension of part b) with a pH adjusting agent to provide a pH of about 6.4 to about 7.0 to the aqueous antacid suspension.
Suitable use of a thickening or suspending agents includes but is not limited to those generally used in aqueous antacid formulations, for example, microcrystalline cellulose, such as Avicel, xanthan gum, guar gum, methyl celluloses such as HPMC and sodium carboxymethylcellulose. Preferably, two suspending agents are used, Avicel and xanthan gum.
An appropriate wetting agent, such as glycerin may be utilized to insure maximum dispersion of the thickening agent in the aqueous system. To such end, the thickening agent, such as xanthan gum is preferably admixed with glycerin in a separate container prior to addition to the suspension/mixture. An alternative to the thickening agent/glycerin premix is the use of appropriate mechanical dispersing means, such as a high shear mixer to assist dispersion of the thickening agent. A commercially available readily dispersible thickening agents may also be used, such as KELTROL RD brand of readily dispersible xanthan gum from Kelco, division of Merck. Such readily dispersible thickening agents may provide adequate dispersion upon direct addition to the aqueous system.
Previous calcium carbonate liquid antacid suspensions have been found to be unstable, and have been found to have to high a resulting pH level. The pH level of the present invention is within the USP standards as has been found to be stable, and can be maintained with an efficient preservative system. Accordingly, a pH adjusting agent is a necessary component of the invention. Citric acid has been found to be a preferred pH adjusting agent, although other carboxylic acids such as tartaric, adipic, benzoic, carbonic, cinnamic, fumaric, glutaric, gluconic, hydroxybenzoic, malonic, malic, phthalic, oxalic, sorbic, succinic and the like may be utilized. The amount of pH adjusting agent should be sufficient to bring about, and maintain the pH of the final product in a range of 7.5 to about 8.7. In general from about 0. 025 to about 0.2% w/w of the pH adjusting agent has been found suitable. As the pH adjusting agent is added at the last step, while mixing, the titrate of the suspension with the pH adjusting agent will be added in an amount sufficient to provide a pH of about 6.4 to 7.0 of the aqueous antacid suspension. It is critical that the pH is measured within 15 minutes after the pH adjusting agent is added. The resulting suspension the next day should have equilibrated to the final desired pH range of from about 7.5 to about 8.7.
Any desired pharmaceutically acceptable adjuvant may be added. For examples, one or more preservatives, such as benzyl alcohol; flavouring agents, such as oil of orange, imitation wintergreen flavour, lemon-lime flavors, mint flavors, or combinations thereof; sorbitol serves to increase shelf life and palatability; wetting agents, an antiflatuent which is preferably simethicone, preferably in an antiflatuent amount of from about 0.1 to about 2.0% w/w is suitable; sweetening agents, such as calcium sacccharin; colouring agents; taste enhancing agents, such as calcium choride; and tetrapotassium pyrophosphate.
A unique aspect of the present invention is the order in which the essential buffering component must be admixed in order to the final suspension to achieve the desired pH range. If the pH adjusting agent is added to the active antacids prior to the last step, it tends to achieve a higher pH or an unstable suspension. It is therefore, critical that all of the components, but for the buffering, be added to the suspension and thoroughly dispersed with the gums prior to the addition of the pH adjusting agent.
A process which combines tetrapotassium pyrophosphate and citric Acid in one solution, at the same time, has a resulting pH which is inconsistent as it can either be below or over the 7.5 to 8.7 limit and takes about 30 days to equilibrate.
In a preferred embodiment, there are a number of separate phases of ingredients which are premixed prior to addition of the liquid antacid suspension. By this is meant, a calcium chloride phase, an first suspending agent phase, a second suspending agent phase, a sweetening phase, an the pH adjusting agent phase. Each individual component is admixed with a formula amount of water and held as a separate phase until addition to the preparation vessel.
While the order of addition to the preparation vessel is the preservative phase followed by the calcium chloride phase, either order is acceptable. To this mixture is added the first suspending agent, such as the Avicel premix, with continual mixing, until the batch becomes smooth and uniform, with no lumps. With continued mixing, the powdered calcium carbonate, USP is mixed. The suspension is stirred until the calcium carbonate is uniformly dispersed and thoroughly coated. To this suspension mixture is added, preferably while stirring is maintained, the second suspending agent, which is preferably xanthan gum. In a preferred aspect the xanthan gum is premixed, not with water but with glycerin. The resulting batch mixture is continued to be stirred until the xanthan gum is adequately hydrated.
To this batch mixture is added the sorbitol solution, USP admixed with formula amounts of water and continued stirring until the batch is uniform. If an antiflatulent, or any other suitable biologically active agents are desired to be added to the suspension, they are added at this stage until the batch is uniform.
While continued mixing, the sweetening phase is added and with continued stirring until uniform. While mixing the optional flavouring agents are also added. Again, the order of addition of these excipients is variable, and may be added at any step herein, a preferred embodiment being in this explicit order. At this time, it is preferred that a batch pH be taken. To this admixture is added the buffering agent phase with an additional formula water. The batch is slowly mixed until uniform. A batch pH is again (or first taken) at this step in the process. To this batch, the pH adjusting phase is now titrated. The Citric Acid Phase is titrated to a target pH of about 6.4 to 7.0. The pH is measured within 15 minutes after the pH adjusting agent is added.
As a guideline, the citric acid phase (CAP) is administered in accordance with the batch pH of the mixture prior to addition of the CAP. If the batch pH before CAP titration is equal to or greater than 7.5, approximately 0.2625% w/w CAP (equivalent to 0.075% w/w Citric Acid) is added, and if necessary more CAP is added in 0.0875% w/w increments (equivalent to 0.025% w/w Citric Acid), until the target pH is reached. The batch is mixed until uniform, or approximately 15 minutes. The pH is measured within 15 minutes after each increment.
If the batch pH before CAP titration is equal to or less than 7.5, approximately 0.0875% w/w CAP (equivalent to 0.025% w/w Citric Acid) is added, and if necessary more CAP is added in increments of 0.0875% w/w CAP until the target pH is reached. The batch is mixed until uniform, or approximately 15 minutes. The pH is measured after each increment.
While not dispositive of the effects of calcium carbonate solubility as it applies to the pH problem for stabilization of liquid antacid suspensions, the following has been observed:
That the reactions associated with calcium carbonate solubility in water are a combination of:
CaC(O)3(solid)⇄Hydration⇄CaC(O)3(hydrate)+H2O+C(O)2⇄Ca(HCO3)2⇄Ca+++HCO3xe2x88x92
CaC(O)3(hydrate)⇄Ca+++CO3xe2x88x92
H2O+C(O)2⇄H3O++HCO3xe2x88x92
The hydration step is the rate limiting step for dissolution.
The solubility of calcium carbonate is about 0.05-0.07% mg/ml at room temperature. The pH of a 10% dispersion of calcium carbonate in water (saturated solution) is about 9.0.
The solubility of calcium carbonate is increased by an increase in carbon dioxide solubilized in the water. The solubility of calcium carbonate decreases with increasing temperatures. The rate of agitation influences the rate of solubility of calcium carbonate. It could take up to 5 days for the saturated solution of calcium carbonate in water to be formed. It takes less than one day if air (carbon dioxide) is passed through the mixture prior to stirring.
Phosphates and anionic surfactants sequester calcium increasing both the rate and extent of solubilization of calcium carbonate. However, some phosphates adhere to the calcium carbonate particle surface inhibiting the sequestration.
Based upon this information, and the assumption that the pH change in the calcium carbonate liquid suspension is due solely to the rate of solubilization of calcium carbonate, the CAP should be added after the saturated solution of calcium carbonate is formed. The emulsifier/texturizer with buffering properties, in this case, tetrapotassium pyrophosphate, could be added first with time need to reach a constant pH. Once the constant pH is reached after the phosphate addition, the pH adjusting agent, CAP, could be added to adjust the pH to a lower USP limit.
Another aspect of the present invention is a stable, high dosage calcium carbonate aqueous antacid formulation which comprises:
Another aspect of the present invention is the stable, high dosage calcium carbonate and simethicone containing aqueous antacid formulation which comprises:
Another aspect of the present invention is a method for neutralizing excess stomach acid in a mammal in need thereof, which method comprises orally administering to said mammal an effective amount of a liquid antacid suspension as noted above.